Two invention pertains to a perforated soft contact lens and a method for manufacturing thereof.
In additional to the required perfect optical performance and a minimum of mechanical irritation, contact lenses should hinder the metabolism of cornea as little as possible to extend their period of continuous wearing without danger of temporary or even lasting unfavorable consequences for eye tissues. The last mentioned condition is attained, at least in part, with soft lenses made of strongly swollen hydrophilic gels, which are relatively well permeable for oxygen and other low-molecular-weight water-soluble metabolities, or with soft lenses made of rubbery silicon polymers, which are at least perfectly permeable for oxygen. However, tear liquid is not changed in a thin liquid film between eye and any of the soft lenses which are always perfectly sucked to the eye surface, so that the transport of metabolites from and to the surface of cornea is limited only to the diffusion mechanism. Consequently, components, which are insoluble in the material of lens and cannot spontaneously penetrate through it, are excluded from this transport. Such components are, e.g., the components of higher molecular weight for hydrophilic-gel lenses and all metabolic components, except oxygen and carbon dioxide, for silicon lenses. These facts represent the most serious shortcoming of soft contact lenses and the only disadvantage in comparison to hard lenses, which never adhere so perfectly to eye as soft lenses and thus enable a relatively good exchange of tear liquid under them during an eye movement. Indeed, the hard lenses cannot compete with soft lenses in the comfort of wearing.
To achieve the direct exchange of tear liquid also with soft lenses, attempts were done with their perforation ("fenestration") without obtaining any important effect. The perforation was always performed outside the optical zone of lens to not impede its optical performance. This failure may be explained by means of the calculated pressure relations under soft lenses (K.Wichterle and O. Wichterle; Lecture at the International Conference on Contact Lenses, Venice, March 1983), which showed that the pressure almost equal zero or even a small overpressure occured at the places where the perforation had been formerly performed. It may be understood, that tear liquid cannot enter under the lens through this perforation.